1. Field of the Invention
The present invention relates to a multiple-duct tube or tube assembly for centrifugal separators for blood in particular. The invention also relates to an apparatus embodying such tube and a method for making such tube.
2. Description of the Prior Art
It is known that many processes which aim to separate different components of a substance are performed by centrifuging the substance itself; this is the case, for example, of blood, which is centrifuged in order to separate various components, such as platelets, plasma and red cells, from whole blood.
Many types of centrifugal separators have been proposed, and one of these is disclosed in U.S. Pat. No. 3,586,413 granted to Adams.
In this type of separator, the multiple-duct tube, which is thus termed since it comprises a plurality of ducts in which the whole blood and the components separated therefrom by centrifugal action is conveyed, and are arranged so as to connect a connector associated with the rotating part of the machine, to a stationary connector, is rotated about the axis of rotation of the centrifugal separator at a rate equal to half the rotation rate of said separator. Branch lines extend from and are variously connected to the stationary connector for conveying blood or blood components to containers or to intracorporeal circulation.
This avoids the twisting of said tube despite the absence of rotating seals of the same on the terminal connectors. This fact is highly positive, since elimination of the rotating seals determines a saving in costs and eliminates the risk of contamination of the processed fluids.
The multiple-duct tube comprised in the described separator, also called "umbilical tube", is typically arranged in a curve which makes it resemble an inverted question mark. During operation, this tube is subjected to combined fatigue stress in which, besides flexure and tortion, the tensile stress due to the action of the centrifugal force is present. This stress can reach even very high values in view of the necessary high rotation rates.
The known art has proposed several different methods for manufacturing umbilical tubes capable of withstanding the stresses without undergoing mishaps.
U.S. Pat. No. 4,906,496 discloses two coaxial tubes with circular walls where the inner tube is kept separate by three dividing elements, so as to define four ducts, three peripheral ones and a central one.
U.S. Pat. No. 4,741,593 discloses three tubes kept parallel inside a sheath, providing a non-monolithic structure; a non-monolithic structure is also disclosed in U.S. Pat. No. 4,865,081.
There is also a type of umbilical tube in which four tubes, mutually joined at a generatrix, are jacketed proximate to their ends and are wrapped by a sheath at their intermediate portion.
In U.S. Pat. No. 4,108,353, U.S. Pat. No. 4,109,852 and U.S. Pat. No. 4,164,318 there is shown an umbilical tube comprising a plurality of ducts within a monolithic structure which has a perfectly circular perimeter in a transverse cross-section and is provided with tapered reinforcements at its ends.
The umbilical tube disclosed in U.S. Pat. No. 4,389,206, U.S. Pat. No. 4,389,207 and U.S. Pat. No. 4,459,169 comprises four plait-wound tubes rigidly associated by glueing.
However, all of the above umbilical tubes have drawbacks. In particular, all have a constructive complexity which arises from the need to give them the necessary stress resistance. This leads to an excessive cost for an element which, as is known, is intended to be used only once. Even despite the constructive complexity, the desired stress resistance is not always achieved in a fully satisfactory manner.
Attempts to reinforce umbilical tubes having a monolithic extruded structure by using glass or carbon fibers have also not yielded the expected results.